1. Field of the Invention
This invention relates to an information signal recording apparatus, and more particularly, to an information signal recording apparatus for recording pilot signals for tracking control on particular areas of a recording medium.
2. Description of the Related Art
A tracking control method has been known in which a dedicated control head is used and a control signal for tracking control is recorded on a dedicated track, as in VHS-type video cassette recorders.
In this method, that uses a dedicated head and track, a track for recording a main (e.g. image) signal as the target of tracking is different from the dedicated track. Accordingly, when high-density recording is performed, accuracy in tracking cannot be sufficiently increased. Furthermore, there is a restriction in hardware because a dedicated head and track are needed.
In another tracking control method, a pilot signal for tracking control is subjected to being frequency multiplexed with an image signal or the like, serving as a main signal, and the resultant signal is recorded on a main track. When reproducing the signal, crosstalk of the pilot signals from adjacent tracks is subjected to frequency separation to obtain a tracking error signal.
In the method where the pilot signal is subjected to frequency multiplexing with the main signal, a dedicated head and track for tracking are not needed. However, since the pilot signal is subjected to frequency multiplexing, it disturbs the main signal. Accordingly, the recording level of the pilot signal must be lower than that of the main signal. As a result, this method has a disadvantage in that an adequate S/N (signal-to-noise) ratio cannot be obtained in the reproduced pilot signal, and stable tracking control cannot be performed.
In order to solve the disadvantages in the above-described two methods, another tracking control method (termed hereinafter an "area-dividing recording method") has been proposed in which a plurality of pilot signals are recorded on particular areas that are divided from the recording areas for a main signal.
In the area-dividing recording method, pilot signals for tracking control and a main information signal are recorded on areas that are divided from each other but are on an identical track. When reproducing the signals, only the pilot signals are separated and extracted from the signal reproduced by a rotating head. Tape running is controlled and adjusted so that the amounts of crosstalk, of the pilot signals from two adjacent tracks, become equal. Thus, proper tracking is realized.
As an example of the area-dividing recording method, a two-frequency area-dividing recording method for recording two kinds of pilot signals will now be explained by reference to the drawings.
FIG. 1 is a diagram showing a recorded pattern on a tape on which recording areas for two kinds of pilot signals f.sub.1 and f.sub.2, having different frequencies, and for a PCM signal (such as an image signal, a sound signal or the like, serving as a main information signal) are divided from each other by performing time-division multiplex recording. FIG. 2 is an enlarged diagram showing the neighborhood of the recording areas for the pilot signals f.sub.1 and f.sub.2.
As shown in FIG. 2, the recording areas for the pilot signals f.sub.1 and f.sub.2 arranged so that an overlapped portion exists between adjacent tracks. The overlapping areas are very small and are located at the two end portions of the respective tracks. Unrecorded areas on which no signals are recorded are provided before and after each of the recording areas for these pilot signals. The scanning direction of a rotating head H and the direction of tape running are indicated by arrows A and B, respectively.
The pilot signals are produced by recording pulse signals in a burst-like form.
FIG. 3 is a block diagram of a tracking control circuit for making the rotating head H follow the tracks recorded as shown in FIG. 1.
Next, an explanation will be provided of the operation of respective units shown in FIG. 3 by reference to a waveform diagram shown in FIG. 4.
The pilot signal reproduced by the rotating head H is amplified by a head amplifier (not shown), and is then supplied to terminal 70 shown in FIG. 3. The pilot signals f.sub.1 and f.sub.2 are separated and extracted by band-pass filters 79 and 81 having passbands for the frequencies of the two kinds of pilot signals, respectively (as shown by S79 and S81 in FIG. 4). Subsequently, envelope waveform signals S80 and S82 of the reproduced pilot signals are obtained by detection circuits 80A and 82A, and low-pass filters 80B and 82B, and are supplied to change-over switches 71 and 72, respectively. The change-over switches 71 and 72 are switched at every half rotation of the rotating head H by switching pulses obtained from terminal 99 in synchronization with the rotation of the rotating head H.
In FIG. 3, a pilot signal (for example, f.sub.1) on a track (termed hereinafter a "home track"), which the rotating head H principally traces, is subjected to waveform shaping by a clipper circuit 78, and the resultant signal is supplied to a sampling pulse generation circuit 73. On the other hand, pilot signals (for example, f.sub.2) obtained as crosstalk from adjacent tracks are supplied to sample-and-hold circuits 75 and 76, where the levels of envelope waveform signals of crosstalk signals from two tracks adjacent to the home track are subjected to sample-and-hold processing with sampling pulses S73 and S74 generated from the sampling pulse generation circuit 73.
A difference between hold levels S75 and S76 becomes a tracking error signal S77, which is supplied to a tracking control circuit 77. The tracking control circuit 77 controls and adjusts tape running so as to minimize the voltage of the tracking error signal, as is well known, to make the tracking of the rotating head H optimum.
In the above-described two-frequency area-dividing recording method, a pilot signal is recorded in a burst-like form on an area joining recording areas on adjacent tracks (see FIG. 2). Therefore, the pilot signal reproduced by the scanning of the rotating head receives noise from adjacent tracks due to transient responses produced at portions where the recording of the pilot signal is started or stopped, as shown in FIGS. 5(A) and 5(B). There is a great influence on a crosstalk signal (a reproduced pilot signal A from tracks adjacent to the home track), which is a very small signal. Hence, the crosstalk method has the disadvantage of a tracking-error voltage that cannot be detected with high accuracy from pilot signals having very small recording areas.
In order to solve the above-described disadvantages, it is possible to expand the recording area for the pilot signal so as to extend the period of time that the crosstalk signal is not influenced by the above-described transient noises. This approach, however, results in reduction of the recording area for the main information signal, causing a disadvantage for high-density recording.